1. Field of the Invention
The present invention relates to a drilling device and a method of creating branches in a bore hole drilled in unstable (unconsolidated) rock. The laying of network lines in the area of a road/street entails the construction of large main lines or network line routes from which small-diameter subsidiary lines branch off during the simultaneous construction of house service lines.
2. Description of the Related Art
On busy roads, digging up roads in order to lay house service lines or construction branch trenches in the road area results in considerable obstructions to traffic and particularly leads to statically adverse encroachments as a result of subsequent subsidence phenomena or the penetration of moisture in the transition zone between the original and repaired road surfaces, running the risk of frost damage. Furthermore, the house service connections in the area of water distribution, natural-gas distribution and for laying electricity or telecommunications lines must each be performed independently of one another, thereby worsening the damage to roads and obstructions to traffic.
In the field of drilling for mineral oil, the development of the North Sea and the use of expensive oil rigs made it necessary to execute a plurality of bores from one of the oil rigs. This "multilateral drilling" therefore became a standard concept in the offshore sector. Whereas the first multilateral bores continued to use adjacent entry bore holes that were each nevertheless independent, techniques were devised on the basis of this practice that used a single entry bore hole from which a plurality of deflected bores are executed. In the "whipstock" technique, use is made of the lateral horizontal deflections deflected by the entry bore in order to pass through hydrocarbon deposits horizontally.
The application of the whipstock technique is performed using an alignable, high-precision whipstock and a drilling system including a screw-type motor and at least two hinge points or titanium screw-type motors without hinge points and stabilizers in the drill rods. There must be a solid bore-hole wall in the area of the branch; this wall may have to be cemented and frequently stabilized by insertion of a branch fitting, too.
The bore-hole branch techniques known in the prior art have so far only been implemented on a large scale in the extraction of oil, petroleum gas or natural gas and have so far been performed either in the rock or in the area of pre-concreted branch sites. The known techniques are therefore inapplicable for the construction of bore-hole branches in the area of network lines in the road area because unconsolidated rock is present here.